The present disclosure relates, in various exemplary embodiments, to photoconductive imaging members. In particular, the present disclosure relates to charge generation layers for photoconductive imaging members wherein the charge generation layers comprise a novel binder composition. More specifically, disclosed herein is a charge generation layer for a photoconductive imaging member comprising a photogenerating pigment and a binder, the binder comprising a modified binder material comprising an electron transport material chemically attached to a polymeric binder material.
In the art of electrophotography, an electrophotographic imaging member or plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation, for example light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles, for example from a developer composition, on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable photosensitive members.
Electrophotographic imaging members are usually multilayered photoreceptors that comprise a substrate support, an electrically conductive layer, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and optional protective or overcoating layer(s). The imaging members can take several forms, including flexible belts, rigid drums, etc. For most multilayered flexible photoreceptor belts, an anti-curl layer is usually employed on the back side of the substrate support, opposite to the side carrying the electrically active layers, to achieve the desired photoreceptor flatness.
One type of multi-layered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a charge blocking layer, a charge generating (photogenerating) layer, and a charge transport layer. The charge transport layer often comprises an activating small molecule dispersed or dissolved in a polymeric film forming binder. Generally, the polymeric film forming binder in the transport layer is electrically inactive by itself and becomes electrically active when it contains the activating molecule. The expression “electrically active” means that the material is capable of supporting the injection of photogenerated charge carriers from the material in the charge generating layer and is capable of allowing the transport of these charge carriers through the electrically active layer in order to discharge a surface charge on the active layer. The multi-layered type of photoreceptor may also comprise additional layers such as an anti-curl backing layer, required when layers possess different coefficient of thermal expansion values, an adhesive layer, and an overcoating layer. Commercial high quality photoreceptors have been produced which utilize an anti-curl coating.
As more advanced, complex, highly sophisticated, electrophotographic copiers, duplicators and printers are developed, greater demands are placed on the photoreceptor to meet stringent requirements for the production of high quality images. To enhance photoreceptor performance, it is desirable to enhance the electrical properties of the photoreceptor. Charge generation layer sensitivity is one particular parameter that is desirable to enhance or improve for improved photoreceptor performance.
One way to enhance charge generation layer sensitivity is by the composition of the photogenerating pigment. For example, the sensitivity of the charge generation layer may be enhanced by mixing high and low sensitivity pigments.
Other attempts to enhance the sensitivity of the charge generation layer have included doping the charge generation layer with electron transporting materials (ETMs). That is, electron transports are physically mixed with a composition comprising a photogenerating pigment and a polymeric binder. Doping the charge generating layer with an electron transport material, however, is limited in its effectiveness to tune or enhance the sensitivity of the charge generation layer. Without being bound to any particular theory, the limited or variable results achieved by doping the charge generation layer with electron transport materials may be due to dispersion-distribution problems. In particular, the tuning effect achieved by physical addition of electron transport materials to a charge generation layer composition may be compromised by the distance between the electron transport materials and the pigment within the solution. That is, because they are free to move around in solution and during the coating process, the electron transport materials do not end up in close enough proximity to the pigment in the final coating to have a significant effect on the sensitivity of the charge generation layer.
It is therefore desirable to provide a charge generation layer with enhanced sensitivity. It is further desirable to provide a way to tune or selectively enhance the sensitivity of a charge generation layer. Along these lines, it is desirable to provide a charge generation layer composition having enhanced sensitivity in a photoconductive imaging member.